Garbage Collection Concepts Quiz Quiz

Evaluate your understanding of garbage collection concepts, including memory management, object lifecycles, and common strategies used by modern programming languages. This quiz is designed to help you assess your knowledge of these essential software development principles.

1. Identifying Unreachable Objects

   Which of the following best describes an object that is eligible for garbage collection in an automatic memory management system?

   1. An object that is still referenced by global variables
   2. An object recently created within a local method
   3. An object stored in a static variable
   4. An object that cannot be reached via any reference from running code

   Explanation: An object becomes eligible for garbage collection when it can no longer be reached by any active references, making it effectively 'unreachable' from running code. Objects referenced by global or static variables are not eligible for collection as they can still be accessed. Newly created objects inside a method remain accessible as long as the method is executing and the reference exists, so they are not immediately eligible for collection. Therefore, only truly unreachable objects meet the requirement.

2. Generational Garbage Collection

   In a generational garbage collection scheme, why are most newly allocated objects initially placed in the 'young' generation?

   1. Because young generation spaces are slower to collect
   2. Because objects in the young generation are stored on the disk
   3. Because only large objects are placed in the young generation
   4. Because most objects become unreachable shortly after creation

   Explanation: The generational garbage collection approach is based on the empirical observation that most objects die young, meaning they become unreachable soon after allocation. Placing new objects in the young generation optimizes collection since short-lived objects can be removed quickly. Collection in the young generation is faster, not slower, so option two is incorrect. Large objects may be handled differently, and young generation objects are not stored on disk, making the other distractors incorrect.

3. Mark-and-Sweep Technique

   In the mark-and-sweep garbage collection process, what is the primary purpose of the 'mark' phase?

   1. To identify all objects still accessible by traversing references
   2. To sort objects according to their reference count
   3. To copy live objects to a new memory area
   4. To physically delete marked objects from memory

   Explanation: The 'mark' phase involves traversing all reachable objects starting from root references and marking those found as accessible or live. Objects are not deleted during this phase—the actual cleanup happens later. Copying objects is part of a different technique called copying collection, and sorting by reference count is not relevant to mark-and-sweep. Thus, only the first option accurately describes the mark phase.

4. Reference Counting Limitation

   Which situation can prevent reference-counting garbage collection from reclaiming memory, potentially causing a memory leak?

   1. When an object has zero references from any part of the code
   2. When two objects refer to each other in a cyclic relationship
   3. When variables are declared as immutable
   4. When all objects have unique string values

   Explanation: Reference counting cannot reclaim objects that refer to one another in a cycle, as their reference counts never reach zero, leading to memory leaks. If an object has zero references, it will be collected correctly. Unique string values do not affect reference counting directly, and immutability of variables isn't related to the problem described. Cyclic relationships are the classic limitation of pure reference-counting systems.

5. Stop-the-World Events

   During some garbage collection processes, what is meant by a 'stop-the-world' event?

   1. Application data is permanently deleted from memory
   2. All application threads are temporarily paused to allow the garbage collector to work safely
   3. All reference variables are reset to null before collection
   4. The garbage collector runs silently without pausing any threads

   Explanation: A 'stop-the-world' event refers to temporarily suspending all program threads, giving the garbage collector exclusive control for activities like marking or sweeping. Application data is not permanently deleted—only unreachable objects are. Reference variables are not universally reset, and garbage collectors that avoid pausing threads are specifically designed to minimize or eliminate such pauses. The correct answer is the pausing of threads.